Since mosaicing is done
mathematically, we are free to choose a still more
sophisticated model than the
affine model, and the model that we use is the plane projective
model. Each image is positioned in terms of its 4 corners (x and y)
giving 8 degrees of freedom. Another interpretation of these 8 dof is as
follows:

translation x

translation y

dilation x

dilation y

shear x

shear y

chirp x

chirp y

The first 6 of these are the traditional affine parameters.
To better understand these first 6, an excellent reference is
the book Linear Algebra.

An automated algorithm
called
CEMENT,
or cement-mix.
Cement-mix was originally developed
to combine and mix images that are ``in the same orbit''
(either video or radar, or combinations of
both) automatically.